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Amplifier circuit for electret condenser microphone

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Publication number
US5577129A
US5577129A US08372884 US37288495A US5577129A US 5577129 A US5577129 A US 5577129A US 08372884 US08372884 US 08372884 US 37288495 A US37288495 A US 37288495A US 5577129 A US5577129 A US 5577129A
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Prior art keywords
circuit
power
supply
amplifier
voltage
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Expired - Fee Related
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US08372884
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Tatsuji Ehara
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NEC Corp
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NEC Corp
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    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03FAMPLIFIERS
    • H03F1/00Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/30Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters
    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03FAMPLIFIERS
    • H03F3/00Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/181Low frequency amplifiers, e.g. audio preamplifiers
    • H03F3/183Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
    • H03F3/187Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only in integrated circuits
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04MTELEPHONIC COMMUNICATION
    • H04M1/00Substation equipment, e.g. for use by subscribers; Analogous equipment at exchanges
    • H04M1/60Substation equipment, e.g. for use by subscribers; Analogous equipment at exchanges including speech amplifiers
    • H04M1/6008Substation equipment, e.g. for use by subscribers; Analogous equipment at exchanges including speech amplifiers in the transmitter circuit

Abstract

An amplifier circuit for an electret condenser microphone includes an operational amplifier, an operational amplifier, a bias circuit, and a power supply circuit. The operational amplifier has an inverting input terminal for receiving an output of a two-wire lead electret condenser microphone and a noninverting input terminal for receiving a bias voltage. The bias circuit divides a power supply voltage to generate the bias voltage. The power supply circuit applies the power supply voltage to the electret condenser microphone through the bias circuit and a first resistor.

Description

This is a continuation of application No. 07/989,824 filed Dec. 14, 1992.

BACKGROUND OF THE INVENTION

The present invention relates to an amplifier circuit for a two-wire lead ECM (Electret Condenser Microphone) and, more particularly, to an amplifier circuit using an operational amplifier.

A conventional amplifier circuit of this type using a single power supply is shown in FIG. 3. A bias voltage applied to a noninverting input terminal 10 of an operational amplifier 2 is generated by a bias circuit 8 constituted by voltage dividing resistors 4 and 5 and a capacitor 6 for reducing power source noise. Since a two-wire lead ECM 3 which applies its output to an inverting input terminal 14 of the operational amplifier 2 receives a power supply voltage and a signal through a common line, a power supply voltage is applied to the ECM 3 by a power supply circuit 9 constituted by resistors 11 and 12 and a capacitor 13. The resistor 12 serves as the load resistor of the power supply circuit 9, and the capacitor 13 reduces noise included in the power supply to prevent the S/N ratio of the ECM 3 from being decreased.

In addition, a capacitor 20 is used for cutting a DC component, and resistors 21 and 22 are used for setting the gain of the operational amplifier 2. Reference numeral 1 denotes an output terminal.

In the above conventional amplifier circuit, the bias circuit 8 for applying a power supply voltage to the noninverting input terminal of the operational amplifier 2 and the power supply circuit 9 for applying a voltage to the ECM 3 are required, and have independent circuit arrangements, respectively. For this reason, in portable equipment such as a portable telephone apparatus which is expected to be compact and lightweight, the number of parts is decreased. In the above conventional arrangement, however, the number of parts of the power supply system circuits 8 and 9 is increased. This is a serious limitation to a decrease in size of the portable equipment.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an amplifier circuit for an electret condenser microphone, in which the size of a power supply system circuit is decreased to reduce the number of parts of the power supply system circuit.

It is another object of the present invention to provide an amplifier circuit for an electret condenser microphone, which does not restrict decreases in size and weight of portable equipment.

In order to achieve the above objects, according to the present invention, there is provided an amplifier circuit for an electret condenser microphone, comprising an operational amplifier having an inverting input terminal for receiving an output from a two-wire lead electret condenser microphone and a noninverting input terminal for receiving a bias voltage, a bias circuit for dividing a power supply voltage to generate the bias voltage, and a power supply circuit for applying the power supply voltage to the electret condenser microphone through the bias circuit and a first resistor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing an amplifier circuit for an ECM according to an embodiment of the present invention;

FIG. 2 is a block diagram showing a portable telephone apparatus in which the amplifier circuit for the ECM of the present invention is used; and

FIG. 3 is a circuit diagram showing a conventional amplifier circuit for an ECM.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an amplifier circuit for an electret condenser microphone according to the present invention, and shows an amplifier circuit, for a two-wire lead ECM, operated by a single power supply. A bias voltage applied to a noninverting input terminal 110 of an operational amplifier 102 is generated by a bias circuit 108 constituted by voltage dividing resistors 104 and 105 and a capacitor 106 for reducing power source noise. Since a bias voltage V1 input to the noninverting input terminal 110 of the operational amplifier 102 is generally selected such that the operational amplifier obtains a maximum output amplitude, the resistances of the resistors 104 and 105 are set to satisfy a condition V1=Vcc/2.

In order to supply a voltage to an ECM 103 for supplying its output to an inverting input terminal 114 of the operational amplifier 102, the output terminal of the bias circuit 108, i.e., the noninverting input terminal 110 of the operational amplifier 102 is connected to the ECM 103 via a resistor 107, and the resistor 107, the resistor 104, and the capacitor 106 constitute a power supply circuit 109. In this case, the resistor 107 serves as the load resistor of the ECM 103, and the capacitor 106 reduces noise included in a power supply voltage to the ECM 103 to prevent the S/N ratio of the ECM 3 from being decreased.

Note that a capacitor 120 is a capacitor for cutting a DC component, and resistors 121 and 122 are used for setting the gain of the operational amplifier 102. Reference numeral 101 denotes an output terminal.

With the above arrangement, the power supply circuit 109 for supplying a power supply voltage to the ECM 103 can be arranged by using the resistor 104 and the capacitor 106 in the bias circuit 108 and additionally arranging the resistor 107. For this reason, some parts of the bias circuit 108 can be used as the parts of the power supply circuit 109, and the number of parts of the bias circuit 108 is decreased by the number of commonly used parts. Therefore, a compact and lightweight portable equipment can be obtained.

In addition, with the above arrangement, power supply noise can be canceled.

The present invention will be described below using a circuit in which the resistances of the resistors 104, 105, 107, 121, and 122 are set to be 4.7 kΩ, 6.8 kΩ, 2.2 kΩ, 22 kΩ, and 270 kΩ, respectively, and the capacitances of the capacitors 106 and 120 are set to be 2.2 μF and 0.01 μF, respectively. When a power supply voltage includes noise, for example, the voltage of noise generated by the noninverting input terminal 110 of the operational amplifier 102 and the voltage of a signal generated by the ECM 103 are represented by Vn and Vs, respectively. In this case, when these voltages are amplified by the circuit, a voltage output to the output terminal 101 of the operational amplifier 102 has a signal component of 12.3 Vs and a noise component of 2.4 Vn.

That is, even when a signal-to-noise ratio (S/N ratio) on the input side is Vs/Vn, an S/N ratio on the output side is 12.3 Vs/2.4 Vn. Therefore, the S/N ratio is increased by 5.125 times.

FIG. 2 shows a portable telephone apparatus of a mobile telephone system in which the amplifier circuit for the ECM according to the present invention is used. The portable telephone apparatus in FIG. 2 comprises a transmitting unit 131, a receiving unit 132, a multiplexer 133, a controller 134, a signal processor 135, an operating unit 136, and a microphone 137, a receiver 138, a power supply unit 139, and an antenna 140.

A speech input from the microphone 137 passes through a bandpass filter, a compressor, and a preemphasis circuit (which are not shown) by the signal processor 135, is FM-modulated in the transmitting unit 131, and is transmitted from the antenna 140 through the multiplexer 133. In addition, a received wave passes from the antenna 140 through the multiplexer 133 and is FM-demodulated in the receiving unit 132. The wave passes through a deemphasis circuit, a bandpass filter, and an expander circuit (which are not shown) by the signal processor 135 and is output as speech from the receiver 138.

The controller 134 designates the channel of the transmitting unit 131, ON/OFF-controls a carrier, designates the channel of the receiving unit 132, controls to monitor received signal strength, designates a speech path of the signal processor 135, processes data with a base station, processes data with the operating unit 136, and controls the power supply unit 139.

The amplifier circuit for the ECM according to the present invention is related to an amplifier circuit incorporated in the microphone 137.

As has been described above, according to the present invention, a resistor is connected between an ECM and the connection point between voltage dividing resistors of a bias circuit, and a power supply voltage is supplied to the ECM through these resistors. For this reason, since some parts of the bias circuit can be used as the parts of a power supply circuit for the ECM, the number of parts of the power supply circuit, and the size of an amplifier circuit can be decreased. As a result, compact and lightweight portable equipment can be advantageously obtained. In addition, the amplifier circuit withstands power supply noise and variations in power supply voltage.

Claims (5)

What is claimed is:
1. An amplifier circuit for an electret condenser microphone, comprising:
an operational amplifier having an inverting input terminal for receiving an output of a two-wire lead electret condenser microphone and a noninverting input terminal for receiving a bias voltage;
a bias circuit for dividing a power supply voltage from a power supply to generate the bias voltage; and
a power supply circuit for applying the power supply voltage to said electret condenser microphone through said bias circuit and a first resistor, wherein
said bias circuit comprises voltage dividing second and third resistors connected in series between said power supply and ground, and a capacitor connected between ground and a connection point between said second and third resistors;
said power supply circuit comprises said second resistor connected to said power supply, said capacitor, and said first resistor connected between said electret condenser microphone and said connection point between said second and third resistors; and
the amplifier circuit has the following characteristics:
the first resistor has a value of 2.2 kΩ
the second resistor has a value of 4.7 kΩ,
the third resistor has a value of 6.8 kΩ, and
the capacitor has a value of 2.2 μF.
2. A circuit according to claim 1, wherein an output terminal for the bias voltage of said bias circuit is connected to said electret condenser microphone through said first resistor.
3. A circuit as claimed in claim 1, wherein
said second and third resistors are directly connected in series to each other, said second resistor being directly connected to said power supply and said third resistor being directly connected to ground;
said capacitor is directly connected to said connection point between said second and third resistors; and
said second resistor and said capacitor are directly connected to said first resistor which is directly connected to said electret condenser microphone.
4. An amplifier circuit for an electret condenser microphone, comprising:
a two-wire lead electret condenser microphone;
an operational amplifier having an inverting input terminal for receiving an output signal from an output terminal of said electret condenser microphone and a noninverting input terminal for receiving a bias voltage;
a bias circuit, for dividing a power supply voltage to generate the bias voltage, comprising first and second resistors connected in series between a power supply and ground, and a capacitor connected in parallel to said second resistor, a connection point between said first and second resistors being connected to said noninverting input terminal of said operational amplifier; and
a third resistor for applying the bias voltage generated by said bias circuit to said electret condenser microphone,
wherein said output terminal of said electret condenser microphone is connected to said noninverting input terminal of said operational amplifier via said third resistor; and
the amplifier circuit has the following characteristics:
the first resistor has a value of 4.7 kΩ,
the second resistor has a value of 6.8 kΩ,
the third resistor has a value of 2.2 kΩ, and
the capacitor has a value of 2.2 μF.
5. A circuit as claimed in claim 4, wherein
said first and second resistors are directly connected to each other, said first resistor being directly connected to said power supply and said second resistor being directly connected to ground;
said capacitor is directly connected to said second resistor;
said connection point between said first and second resistors is directly connected to said noninverting input terminal of said operational amplifier; and
said resistor for applying the bias voltage is directly connected to said connection point between said first and second resistors and directly connected to said electret condenser microphone.
US08372884 1991-12-12 1995-01-13 Amplifier circuit for electret condenser microphone Expired - Fee Related US5577129A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
JP35065691A JP2734265B2 (en) 1991-12-12 1991-12-12 Electret condenser microphone for amplification circuit
JP3-350656 1991-12-12
US98982492 true 1992-12-14 1992-12-14
US08372884 US5577129A (en) 1991-12-12 1995-01-13 Amplifier circuit for electret condenser microphone

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US08372884 US5577129A (en) 1991-12-12 1995-01-13 Amplifier circuit for electret condenser microphone

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US98982492 Continuation 1992-12-14 1992-12-14

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US5577129A true US5577129A (en) 1996-11-19

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JP (1) JP2734265B2 (en)
EP (1) EP0546571B1 (en)

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5832076A (en) * 1996-08-07 1998-11-03 Transcrypt International, Inc. Apparatus and method for determining the presence and polarity of direct current bias voltage for microphones in telephone sets
US5946392A (en) * 1996-11-22 1999-08-31 Lucent Technologies Inc. Telephone handset interface device
FR2789242A1 (en) * 1999-01-28 2000-08-04 St Microelectronics Sa Electronic circuit for amplification of microphone signal with neutralization of supply voltage noise, comprising differential amplifier with pull-up voltage coupled to two inputs by resistor
US6160450A (en) * 1999-04-09 2000-12-12 National Semiconductor Corporation Self-biased, phantom-powered and feedback-stabilized amplifier for electret microphone
US6266424B1 (en) * 1996-11-13 2001-07-24 Vxi Corporation Electret microphone circuit with low battery disable
US20020071578A1 (en) * 2000-07-05 2002-06-13 Van Der Zwan Eric Jurgen A/D converter with integrated biasing for a microphone
US20020085726A1 (en) * 2001-01-04 2002-07-04 Fuqua Kenton Michael Apparatus, system and method for capturing sound
US20020125949A1 (en) * 2001-03-09 2002-09-12 Stenberg Lars J. Electret condensor microphone preamplifier that is insensitive to leakage currents at the input
US6453048B1 (en) * 1998-05-07 2002-09-17 Kabushiki Kaisha Audio-Technica Impedance converter for a condenser microphone
US20030223592A1 (en) * 2002-04-10 2003-12-04 Michael Deruginsky Microphone assembly with auxiliary analog input
US20050220314A1 (en) * 2004-03-30 2005-10-06 Werner Lang Polarization voltage setting of microphones
US20060285699A1 (en) * 2002-01-03 2006-12-21 Fuqua Kenton M Apparatus, system and method for capturing sound
KR100787012B1 (en) 2005-01-06 2007-12-18 엔이씨 일렉트로닉스 가부시키가이샤 Voltage supply circuit, power supply circuit, microphone unit using the same, and microphone unit sensitivity adjustment method
US20080317262A1 (en) * 2005-02-18 2008-12-25 Jens Schlichting Microphone Having an Output Signal Amplifier
US20090046870A1 (en) * 2007-08-13 2009-02-19 Turnbull Robert R Auto bias microphone system for use with multiple loads and method of forming same
US20090214057A1 (en) * 2008-02-21 2009-08-27 Mediatek Inc. Microphone bias circuits
US20100145541A1 (en) * 2007-08-02 2010-06-10 Endress + Hauser Flowtec Ag Fieldbus unit for a two-conductor fieldbus
US20100290649A1 (en) * 2009-05-05 2010-11-18 Sennheiser Electronic Gmbh & Co. Kg Power supply device for a microphone
US20110096945A1 (en) * 2001-02-02 2011-04-28 Fuerst Claus Erdmann Microphone unit with internal A/D converter
US8027489B1 (en) * 2006-07-07 2011-09-27 Analog Devices, Inc. Multi-voltage biasing system with over-voltage protection

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2722636B1 (en) * 1994-07-15 1996-09-20 Le Tourneur Gregoire A sound pickup by electret microphone
EP0930802B1 (en) * 1997-12-19 2008-09-03 Texas Instruments Inc. Microphone bias current measurement circuit
US6731748B1 (en) * 1998-11-30 2004-05-04 Qualcomm Incorporated Audio interface for satellite user terminals
JP2012019543A (en) * 2001-02-02 2012-01-26 Sonion Aktie Selsxab Microphone with built-in a/d converter
JP2009239202A (en) 2008-03-28 2009-10-15 Sanyo Electric Co Ltd Amplifying element and manufacturing method thereof
US20100073079A1 (en) 2008-09-24 2010-03-25 Sony Ericsson Mobile Communications Ab Bias arrangement and apparatus
JP2010103842A (en) 2008-10-24 2010-05-06 Sanyo Electric Co Ltd Amplifier device
CN102833650A (en) * 2012-09-14 2012-12-19 南京莱斯信息技术股份有限公司 AV (Audio/Video) control platform with microphone input module

Citations (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE242708C (en) *
US3789155A (en) * 1970-07-24 1974-01-29 Post Office Side-tone reducing circuit for a telephone subscribers instrument
GB1441624A (en) * 1972-08-23 1976-07-07 Int Standard Electric Corp Sound-signal receiver with an electrostatic microphone
US3974344A (en) * 1974-03-05 1976-08-10 Telefonaktiebolaget L M Ericsson Electronic speech circuit for a central battery telephone set
US4281221A (en) * 1978-07-12 1981-07-28 Societa Italiana Telecomunicazioni Siemens S.P.A. Condenser microphone
US4303805A (en) * 1979-05-21 1981-12-01 United Networks, Inc. Subscriber station network
US4314107A (en) * 1979-12-26 1982-02-02 United Networks, Inc. Subscriber station networks
US4326106A (en) * 1979-02-03 1982-04-20 Licentia Patent-Verwaltungs Gmbh Telephone amplifier circuit
US4518829A (en) * 1984-04-02 1985-05-21 Gte Communications Systems Corporation Two terminal microphone active load gain regulation circuit
US4536888A (en) * 1981-08-21 1985-08-20 Plantronics, Inc. Voice communication instrument system with line-powered receiver conditioning circuit
US4541112A (en) * 1982-06-14 1985-09-10 Georg Neumann Gmbh Electroacoustic transducer system
US4640993A (en) * 1984-06-28 1987-02-03 International Standard Electric Corporation Telephone subscribers' circuits
US4672663A (en) * 1985-06-28 1987-06-09 Mitel Corporation Telephone handset detector
US4757545A (en) * 1983-02-25 1988-07-12 Rune Rosander Amplifier circuit for a condenser microphone system
EP0305301A1 (en) * 1987-07-21 1989-03-01 Sgs-Thomson Microelectronics S.A. Signal compressor circuit, in particular for telephone set
US4922547A (en) * 1986-12-15 1990-05-01 Nec Corporation Microphone circuit
FR2651120A1 (en) * 1989-08-24 1991-03-01 Rosenfeld Igal Device to stop people from snoring without waking them
US5036536A (en) * 1990-02-20 1991-07-30 Plantronics, Inc. Electret microphone transmitter for use in telephone circuits

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0389608A (en) * 1989-08-31 1991-04-15 Mitsumi Electric Co Ltd High input impedance amplifier

Patent Citations (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE242708C (en) *
US3789155A (en) * 1970-07-24 1974-01-29 Post Office Side-tone reducing circuit for a telephone subscribers instrument
GB1441624A (en) * 1972-08-23 1976-07-07 Int Standard Electric Corp Sound-signal receiver with an electrostatic microphone
US3974344A (en) * 1974-03-05 1976-08-10 Telefonaktiebolaget L M Ericsson Electronic speech circuit for a central battery telephone set
US4281221A (en) * 1978-07-12 1981-07-28 Societa Italiana Telecomunicazioni Siemens S.P.A. Condenser microphone
US4326106A (en) * 1979-02-03 1982-04-20 Licentia Patent-Verwaltungs Gmbh Telephone amplifier circuit
US4303805A (en) * 1979-05-21 1981-12-01 United Networks, Inc. Subscriber station network
US4314107A (en) * 1979-12-26 1982-02-02 United Networks, Inc. Subscriber station networks
US4536888A (en) * 1981-08-21 1985-08-20 Plantronics, Inc. Voice communication instrument system with line-powered receiver conditioning circuit
US4541112A (en) * 1982-06-14 1985-09-10 Georg Neumann Gmbh Electroacoustic transducer system
US4757545A (en) * 1983-02-25 1988-07-12 Rune Rosander Amplifier circuit for a condenser microphone system
US4518829A (en) * 1984-04-02 1985-05-21 Gte Communications Systems Corporation Two terminal microphone active load gain regulation circuit
US4640993A (en) * 1984-06-28 1987-02-03 International Standard Electric Corporation Telephone subscribers' circuits
US4672663A (en) * 1985-06-28 1987-06-09 Mitel Corporation Telephone handset detector
US4922547A (en) * 1986-12-15 1990-05-01 Nec Corporation Microphone circuit
EP0305301A1 (en) * 1987-07-21 1989-03-01 Sgs-Thomson Microelectronics S.A. Signal compressor circuit, in particular for telephone set
FR2651120A1 (en) * 1989-08-24 1991-03-01 Rosenfeld Igal Device to stop people from snoring without waking them
US5036536A (en) * 1990-02-20 1991-07-30 Plantronics, Inc. Electret microphone transmitter for use in telephone circuits

Non-Patent Citations (5)

* Cited by examiner, † Cited by third party
Title
Langford Smith (ed.), Radiotron Designer s Handbook, 1968, pp. 535 539. *
Langford-Smith (ed.), Radiotron Designer's Handbook, 1968, pp. 535-539.
Tremaine, Audio Cyclopedia, 1980, pp. 549 & 607. *
Tremaine, Audio Cyclopedia, 1980, pp. 549 607. *
Tremaine, Audio Cyclopedia, 1980, pp. 549-607.

Cited By (33)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5832076A (en) * 1996-08-07 1998-11-03 Transcrypt International, Inc. Apparatus and method for determining the presence and polarity of direct current bias voltage for microphones in telephone sets
US6266424B1 (en) * 1996-11-13 2001-07-24 Vxi Corporation Electret microphone circuit with low battery disable
US5946392A (en) * 1996-11-22 1999-08-31 Lucent Technologies Inc. Telephone handset interface device
US6453048B1 (en) * 1998-05-07 2002-09-17 Kabushiki Kaisha Audio-Technica Impedance converter for a condenser microphone
US6842525B1 (en) 1999-01-28 2005-01-11 Stmicroelectronics Sa Signal amplification circuit and process for neutralizing noise from a power supply voltage
FR2789242A1 (en) * 1999-01-28 2000-08-04 St Microelectronics Sa Electronic circuit for amplification of microphone signal with neutralization of supply voltage noise, comprising differential amplifier with pull-up voltage coupled to two inputs by resistor
US6160450A (en) * 1999-04-09 2000-12-12 National Semiconductor Corporation Self-biased, phantom-powered and feedback-stabilized amplifier for electret microphone
US20020071578A1 (en) * 2000-07-05 2002-06-13 Van Der Zwan Eric Jurgen A/D converter with integrated biasing for a microphone
US7489791B2 (en) * 2000-07-05 2009-02-10 Koninklijke Philips Electronics N.V. A/D converter with integrated biasing for a microphone
US20020085726A1 (en) * 2001-01-04 2002-07-04 Fuqua Kenton Michael Apparatus, system and method for capturing sound
US20110096945A1 (en) * 2001-02-02 2011-04-28 Fuerst Claus Erdmann Microphone unit with internal A/D converter
US8649528B2 (en) 2001-02-02 2014-02-11 Techtronic A/S Microphone unit with internal A/D converter
WO2002073792A2 (en) * 2001-03-09 2002-09-19 Techtronic A/S An electret condensor microphone preamplifier that is insensitive to leakage currents at the input
WO2002073792A3 (en) * 2001-03-09 2003-01-09 Lars Stenberg An electret condensor microphone preamplifier that is insensitive to leakage currents at the input
US20020125949A1 (en) * 2001-03-09 2002-09-12 Stenberg Lars J. Electret condensor microphone preamplifier that is insensitive to leakage currents at the input
US7110560B2 (en) * 2001-03-09 2006-09-19 Sonion A/S Electret condensor microphone preamplifier that is insensitive to leakage currents at the input
US20060285699A1 (en) * 2002-01-03 2006-12-21 Fuqua Kenton M Apparatus, system and method for capturing sound
US20030223592A1 (en) * 2002-04-10 2003-12-04 Michael Deruginsky Microphone assembly with auxiliary analog input
US20050220314A1 (en) * 2004-03-30 2005-10-06 Werner Lang Polarization voltage setting of microphones
US7835531B2 (en) * 2004-03-30 2010-11-16 Akg Acoustics Gmbh Microphone system
US20050231873A1 (en) * 2004-03-30 2005-10-20 Kurt Nell Microphone system
US7620189B2 (en) * 2004-03-30 2009-11-17 Akg Acoustics Gmbh Polarization voltage setting of microphones
KR100787012B1 (en) 2005-01-06 2007-12-18 엔이씨 일렉트로닉스 가부시키가이샤 Voltage supply circuit, power supply circuit, microphone unit using the same, and microphone unit sensitivity adjustment method
US20080317262A1 (en) * 2005-02-18 2008-12-25 Jens Schlichting Microphone Having an Output Signal Amplifier
US8027489B1 (en) * 2006-07-07 2011-09-27 Analog Devices, Inc. Multi-voltage biasing system with over-voltage protection
US20100145541A1 (en) * 2007-08-02 2010-06-10 Endress + Hauser Flowtec Ag Fieldbus unit for a two-conductor fieldbus
US9035483B2 (en) * 2007-08-02 2015-05-19 Endress + Hauser Flowtec Ag Fieldbus unit for a two-conductor fieldbus
US8243956B2 (en) * 2007-08-13 2012-08-14 Gentex Corporation Auto bias microphone system for use with multiple loads and method of forming same
US20090046870A1 (en) * 2007-08-13 2009-02-19 Turnbull Robert R Auto bias microphone system for use with multiple loads and method of forming same
US20090214057A1 (en) * 2008-02-21 2009-08-27 Mediatek Inc. Microphone bias circuits
US8059836B2 (en) * 2008-02-21 2011-11-15 Mediatek Inc. Microphone bias circuits
US8379896B2 (en) * 2009-05-05 2013-02-19 Sennheiser Electronic Gmbh & Co. Kg Power supply device for a microphone
US20100290649A1 (en) * 2009-05-05 2010-11-18 Sennheiser Electronic Gmbh & Co. Kg Power supply device for a microphone

Also Published As

Publication number Publication date Type
EP0546571A1 (en) 1993-06-16 application
EP0546571B1 (en) 1997-03-12 grant
JP2734265B2 (en) 1998-03-30 grant
JPH05167358A (en) 1993-07-02 application

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